Yesterday I reviewed a study on fasted exercise and glucose tolerance. Please read it now if you haven’t done so. Although the investigators were interested in finding out whether fasted state exercise is more potent than exercise in the fed state to rescue whole-body glucose tolerance and insulin sensitivity during a period of hyper-caloric fat-rich diet and not body composition changes, the body composition changes at the end of the study were quite interesting, so today I will briefly discuss what happens when you ingest carbohydrates before and during a workout.
In yesterdays review both groups followed the same exercise program but the diet was different. The fasted group (exercise performed in a fasted state) but consuming a hyper-caloric fat-rich diet (50% of calories came from fat, and consuming 30% more calories than required to maintain a stable weight).Group two, the carbohydrate group, which ate breakfast 90 minutes before exercise consisting of 675 calories with a macronutrient ratio of 70% carbohydrates, 15% fat, 15% protein (118 grams of carbs!!!) plus consuming a beverage containing 1gram of maltodextrin per kilogram of bodyweight during exercise, and finally group three, no training, but same diet as group one and two.
At the end of the 6 week study, the fasted exercise group gained 0.7 kilograms (kg) in bodyweight, and the carbohydrate group gained 1.4 kgs of bodyweight. So how did the carbohydrate group gain double the weight even though they consumed about a 1000 less calories per day? It has long been recognized that carbohydrate ingestion during exercise reduces fat oxidation during exercise. It has also been shown that a high carbohydrate dense meal can suppress fat oxidation for at least four hours after a meal. It doesn’t take much of a rise in insulin (carbohydrate ingestion raises insulin) to slow down fat oxidation. Innumerable amount of studies have proven that carbohydrate ingestion shortly before (2-4 hours) and during exercise can suppress fat oxidation during exercise. One study that had volunteers consume carbohydrates during exercise report “glucose ingestion during moderate-intensity exercise inhibits the expression of genes involved in the transport and oxidation of lipids”. So by having higher insulin levels at the time of exercise you are suppressing these favorable adaptive changes in fat metabolism that you’re hoping for, and you start to accumulate fat. That’s exactly what happened to the carbohydrate group in yesterdays review even though they were training intensely 4 times a week.
What’s the solution? If you’re on a carbohydrate dense diet (300 plus grams a day) I would suggest you lower your carbohydrates and increase your fat and protein consumption. The lower your carbohydrate intake is the less fat oxidation suppression you will experience. I would also suggest you don’t time a carbohydrate dense meal too close to a workout. Regardless of which diet you’re currently on, fasted exercise can work great for dropping excess fat, especially when doing cardiovascular / endurance exercise. There are more solutions to this problem and I will write about them in the future.,
